1. Field of the Invention
The present invention relates to an image display apparatus, an imaging apparatus, an image display method, a control method for the imaging apparatus, and a program.
2. Description of the Related Art
Nowadays, cellular phones having a wireless communication function are generally used in sharing or exchanging images and messages between users. Such a message exchange system is useful in attaching a text to a captured image and transmitting the text-attached image.
On the other hand, a technique called augmented reality technique has become popular these days. The augmented reality technique superimposes computer graphics (CG) on an image captured by a camera when it is displayed. By using this technique, the provider of the augmented reality system can provide the user with a feeling that the CG-superimposed image is the real image.
In recent years, a message exchange system using augmented reality technique which combines the above-described two systems is also used. According to this message exchange system, if a user of an information terminal sees one's surroundings using a camera which is integrated in the terminal, the user can see messages posted by other users or himself via the display screen. According to such a message exchange system using the augmented reality technique, the posted messages are displayed at the positions corresponding to the position information acquired from a position information acquisition unit in the information terminal. The position information acquisition unit is, for example, based on the global positioning system (GPS). If the user in the vicinity of the arranged message looks around while holding the information terminal, the user can see a message-added CG on the display screen of the information terminal in the direction where the message was posted.
With respect to such a conventional message exchange system, the message is displayed by the processes described below. First, if a poster desires to post a message, the poster starts a message exchange application and touches a posting button. Then, the poster inputs a text message to be posted. At this time, if the user desires to attach a photograph to the text, the poster presses the shooting button and performs imaging. Then, when the poster touches the send button, the input text and the photograph which was taken are transmitted to a message exchange server by wireless communication. When the text and the photograph are transmitted, position information of the information terminal of the poster is also transmitted in association with the text and the photograph. The position information is acquired by a position information acquisition unit of the information terminal.
If another user desires to view the posted message, the following processing is performed. First, the user starts the message exchange application by operating the information terminal. When the application is started, the position information of the information terminal of the user is transmitted to the message exchange server by the information terminal. Further, the information terminal downloads a list of messages associated with the position of the user, for example, within 500 meters from the position of the user, by wireless communication.
Some of the messages of the downloaded group may be associated with the position information of where the messages were posted. If the user holds the information terminal in the direction the user desires to see, an image captured in that direction is displayed on the display screen of the information terminal. Further, if a posted message exists in that direction, the posted message is superimposed on the captured image. Before displaying such a message, the information terminal determines whether a message exists in the field of view based on information acquired from a built-in electronic compass and an orientation sensor.
According to the conventional message exchange system, the position information attached to the message when the message is posted is the position information of the terminal acquired by the GPS. Thus, if the user captures an image of an advertising sign of a store, inputs “I visit this store frequently.” as a message, and posts it, according to this method, the position associated with the message is not the position of the store but the position where the user captured the image. Further, since the information output by the position information acquisition unit and the electronic compass includes some error, there is a possibility of a position error between the posting time and the display time. Thus, the message is not always displayed at the position designated by the poster.